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Closed 2 years ago.
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Can some one please tell me how can I find the following.
List from /etc/passwd the UID and the user having the highest UID.
cat /etc/passwd | awk -F: '{print $3,$1}' | sort -n | tail -n 1
Instead of reading /etc/passwd, it would be better to get the output from
getent passwd
As you could be using another source of UIDs via nsswitch, such as LDAP.
/etc/passwd contains user information separated by colons. The user id is in the third column.
The sort command line tool can be used to sort the lines of a file. It has options, to choose which separator the columns are separated by, which column to sort by and whether to sort numerically or alphabetically.
So you can use sort to sort /etc/passwd by user id and then use tail to get the last line from that, which will contain the user with highest id.
getent passwd | awk -F : '$3>h{h=$3;u=$1}END{print h " " u}'
The getent output needs to be sorted for the awk command.
In addition, I found that nfsnobody (on Linux) can be ignored and the next highest UID is what is often needed. So this worked well:
getent passwd |sort -t: -k3 -n |awk -F: '$3>h{ph=h;pu=u;h=$3;u=$1}END{print h,u"\n"ph,pu}'
65534 nfsnobody 1002 user2
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Closed 11 months ago.
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A command in linux to list the top N most frequent commands used in your zsh.
In zsh
fc -ln 0 | awk '{print $1}' | sort | uniq -c | sort -nr | head -<X>
fc -ln 0 - show the history
awk - prints only the command without the arguments
sort - for using the next pipe
uniq -c - count uniques commands
sort -rn - sort by number in reverse
head -<X> - list the top X
similar to bash
history | awk '{print $2}' | sort | uniq -c | sort -rn| head -<X>
Special thanks to #ericbn
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Closed 4 years ago.
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find . -name "recovery_script" | xargs
I try to execute but it only prints it. How can I run it parallel ?
find . -name "recovery_script" | xargs -n1 -P8 sh
for 8 processes in parallel.
Provided there are at least 8 places where "recovery_script" can be found.
The -n1 argument is necessary to feed one argument at a time to sh. Otherwise, xargs will feed a reasonable number of arguments all at once to sh, meaning it's trying to execute something like
sh dir1/recovery_script dir2/recovery_script dir3/recovery_script ...
instead of
sh dir1/recovery_script
sh dir2/recovery_script
sh dir3/recovery_script
...
in parallel.
Bonus: your command can be longer than just a single command, including options. I often use nice to allow other processes to still continue without problems:
find . -name "recovery_script" | xargs -n1 -P8 nice -n19
where -n19 is an option to nice, not to xargs.
(Aside: if you ever use wildcards for -name in find, use the -print0 option to find, and the -0 option to xargs: that separates output and input by the null character, instead of whitespace (since the latter may be part of the filename). Since you search for the full name here, that is not a problem.)
From the xargs manual page:
SYNOPSIS: xargs ... [command [initial-arguments]]
and
... and executes the command (default is /bin/echo) one or more times with any initial-arguments followed by items read from standard input.
The default behaviour is thus to echo whatever arguments you give to xargs. Providing a command like sh (perhaps depending on what executable you're trying to run) then works.
This solution is not using xargs but a simple bash script. Maybe it can help:
#!/bin/sh
for i in $(find -name recovery_script)
do
{
echo "Started $i"
$i
echo "Ended $i"
} &
done
wait
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I am trying to grep a list of IDs present in file1 from file2
I write:
grep -f file1 file2
The command gets stuck as if perpetually in the run phase.
Then I try:
fgrep -f file1 file2
This works in a flash.
The man page of grep says that fgrep is same as "grep -f". But then how come I get no output for "grep -f"
You cite the man page incorrectly! What is written there is this:
fgrep is the same as grep -F
Note the uppercase -F which is quite different to -f!
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I would like to grep a pattern from multiple log files which are being constantly updated by some processes and tail the output of this grep continuosly.
Below command doesnt work and I get
tail: warning: following standard input indefinitely is ineffective
tail -f | grep --line-buffered "Search this: " /var/links/proc2/id/myprocess*/Daily/myprocess*.log
Can someone help sort this out?
You should have a look at multitail tool (Install using sudo apt-get install multitail)
In short, with multitail, you need to use the --mergeall flag for viewing output of all in one place
multitail --mergeall /var/links/proc2/id/myprocess*/Daily/myprocess*.log | grep --line-buffered "Search this: "
You can do the same without using grep
multitail -E "Search this: " --mergeall /var/links/proc2/id/myprocess*/Daily/myprocess*.log
To view the output individually using multitail, this will give the filename as well.
multitail -E "Search this: " /var/links/proc2/id/myprocess*/Daily/myprocess*.log
the mistake is that you give the files to the grep command and not the tail.
the tail -f needs to get the files as input. try:
tail -f /var/links/proc2/id/myprocess*/Daily/myprocess*.log | grep --line-buffered "Search this: "
to get also the file names (however it will not be like grep output it is):
tail /var/links/proc2/id/myprocess*/Daily/myprocess*.log | grep --line-buffered -e'^==> .* <==$' -e'Search this: '
This is an interesting question and the simple answer should be: Use the prefix switch with tail, but unfortunately this is currently not implemented in most versions of tail.
As I see it, you have two options: adapt the standard tools to the task (see Udys answer) or write your own tool with your favorite scripting/programming language.
Below is one way you could do it with the File::Tail::Multi module for perl. Note that you may need to install the module from CPAN (cpan -i File::Tail::Multi).
Save the following script e.g. mtail to your executable path and make the script executable.
#!/usr/bin/env perl
use File::Tail::Multi;
$| = 1; # Enable autoflush
$tail = File::Tail::Multi->new(RemoveDuplicate => 0,
OutputPrefix => 'f',
Files => \#ARGV);
while(1) { $tail->read; $tail->print; sleep 2 }
Change OutputPrefix to 'p' if you prefer full path prefixes.
Run it like this:
mtail /var/links/proc2/id/myprocess*/Daily/myprocess*.log | grep --line-buffered "Search this: "
You do not need to specify --line-buffered when grep is the last command, so this is sufficient:
mtail /var/links/proc2/id/myprocess*/Daily/myprocess*.log | grep "Search this: "
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Using UNIX Scripting it is possible to remove all the firsts characters from a file till a specific character is found ?
I have a file with "garbage" at the beginning. I want to remove that "garbage, meaning that all the character till the first "{" must be removed. How can I do this ?
cat file.txt | grep -A 1000000000 '{' | sed '1 s/^[^{]*//'
This will print the changed contents (i. e. without the garbage) to stdout. You can redirect this using > outfile.txt appended to the command:
cat file.txt | grep -A 1000000000 '{' | sed '1 s/^[^{]*//' > outfile.txt
And if you want to change the file in-place, this can be done by renaming the outfile.txt to the original name file.txt afterwards:
mv outfile.txt file.txt